Equipment subject to failure includes, but is not limited to, water mains, water or gas pipes, fire hydrants, tunnels, bridges and electrical power subsystems and transmission lines. The societal impacts of equipment failures are well known. For example, a water main failure can result in unavailability of water supply, water losses, road closures and water contamination. Thus, the prevention of equipment failure and efficient maintenance of equipment has been one of the considerable infrastructure issues facing city and municipal authorities.
Traditionally, municipalities have taken reactive actions in repairing, rehabilitating and replacing deteriorated public facilities. However, with the recent availability of geographic information systems, e.g., products from CARIS (Computer Aided Resource Information Systems) and computer-based maintenance management systems, e.g., NEXGEN® Asset Management 2011, an increasing number of municipalities have started to collect equipment failure and maintenance records, build models for predicting breakage of equipment, and plan proactive maintenance interventions.
As an example, maintenance systems have begun to store data on water pipes, for example, diameter, material, failure times and causes, in databases, and have started using this data to estimate the mean residual life of each item of equipment for preventive replacement and planning purposes. Given the lack of past record keeping, a length (e.g., 8 years) of an observation window (i.e., time duration during which maintenance actions on equipment are recorded in a database) is short compared to the average service life of the equipment (e.g., 100 years in the case of water pipes). Information on failures that occurred before the start of the observation windows is typically not available.